## C# program to check if a user input number is prime:

In this post, we will learn how to check if a user input number is *prime* or not. It will take one number as input, check it if it is *prime* or not and print this result.

### C# program:

A number is called a *prime number* if it has only by itself and *1*. For example, *2,3,5,7,11* are prime numbers but *98* is not.

Below is the complete program:

```
using System;
public class Program
{
private static bool isPrime(int num){
for(int i = 2; i<= num/2; i++){
if(num % i == 0){
return false;
}
}
return true;
}
public static void Main()
{
int num;
Console.WriteLine("Enter the number to check : ");
num = int.Parse(Console.ReadLine());
if(isPrime(num)){
Console.WriteLine("{0} is a prime number",num);
} else {
Console.WriteLine("{0} is not a prime number",num);
}
}
}
```

Here,

*isPrime*is used to check if a given number is prime or not. It returns*true*if it is prime, else*false*. We can check up to*number/2*if any one can divide the number or not. It makes the*for loop*smaller.- It is asking the user to enter a number to check. Using
*ReadLine()*, it reads that number and stored it in*num*. - Using
*isPrime*, it checks if it is prime or not. - Based on the return value of
*isPrime*, it prints one message.

### Sample output:

It will print output as like below:

```
Enter the number to check :
98
98 is not a prime number
Enter the number to check :
97
97 is a prime number
```